During the past decade, soft lithography has developed to a versatile technique for fabricating chemically micro- and nanostructured surfaces [1,2]. Among several techniques known collectively as soft lithography, micro-contact printing (μCP) has become the most commonly used method [1]. A patterned polymer stamp is covered with an ink of molecules using either contact inking or wet inking. In contact inking the solvent is reduced to the dry state while the molecules self assemble on an inkpad. The molecules are transferred onto the stamp under ambient conditions by bringing the stamp and the inkpad into conformal contact. In the wet inking process, the ink is poured over the stamp and then reduced under a stream of nitrogen to a dry state. In both cases the molecules are on the stamp prior to the transfer onto a substrate. For the transfer of the ink onto the substrate, stamp and substrate are brought into conformal contact with a substrate for the transfer of the molecules from the stamp to the substrate [3,4].
Recently, also proteins have been transferred to a variety of substrates [5-7]. The advantage of μCP thereby is the direct, fast and gentle transfer of proteins, however, all μCP-techniques reported so far ultimately lead to a denaturation of the printed proteins. Native proteins immobilized onto modified surfaces are of major interest for sensor technology, cell culturing and micro-biology. One application is e.g., the patterning of growth factor proteins on silicon oxide for guiding cell growth [8].
A critical issue for the immobilization of biomolecules, e.g. proteins, nucleic acids etc. on surfaces is their denaturation and hence the loss of the functionality after their immobilization. The functionality, as e.g. in the case of cytochrome c (cyt c), may depend on the orientation and conformation of the protein on the surface. So far, the immobilization and redox activity of cyt c has been investigated on chemically modified Au surfaces [9-11] and on ITO [12]. Runge et al. reported a process for the transfer for cyt C molecules onto ITO surfaces, in which the proteins are dried on the stamp [12]. For ITO-surfaces it could be demonstrated that the reactivity of the proteins depend on the surface modification of the stamps used for the process [11].
In addition to transferring proteins, a method for transfer-printing of highly aligned DNA nanowires has been described by Nakao et al. [13] using PDMS stamps. In this method hydrodynamic forces are used to align DNA on PDMS. After the alignment step the PDMS stamp is brought into conformal contact with a mica sheet for the transfer of DNA onto mica. AFM images showed that the apparent height of the as transferred DNA is between 0.27 and 0.35 nm, indicating that the DNA molecules are probably elongated and possibly sheared as a result of the hydrodynamic forces.
However, all the above described inking methods used in the prior art cause denaturation of the protein(s) and loss of their activity.